PL and EL quenching due to thin metal films in conjugated polymers and polymer LEDs

We report quenching of photoluminescence (PL) and electroluminescence (EL) in conjugated polymers and polymer light-emitting diodes (LEDs) in the proximity of a thin metal film. We have used films of MEH-CN-PPV and DHeO-CN-PPV on gold or aluminium layers of 2 nm to 35 nm thickness. We demonstrate that the presence of a thin metal film reduces the PL quantum efficiency of polymer films as far as 60nm away from the metal. Within a critical distance of 20nm almost all luminescence is quenched. We show that in PPV/MEH-CN-PPV double layer LEDs the position of the recombination zone at the polymer-polymer interface relative to the aluminium electrode is crucial to their increased EL efficiencies.